Elongated interventional device with variable stiffness

ABSTRACT

An elongated device, e.g. an interventional guide wire or catheter, comprises an optical fiber (OF) arranged to allow transmission of light to phase change material (PCM) arranged long the elongated device, for optically heating the phase change material (PCM) to change its stiffness from one stiffness value to a different stiffness value. Using distributed tilted or blazed Bragg gratings with light wavelength dependent unique grating periods along the optical fiber, it is possible to provide a guide wire or catheter which can be stiffness controlled at selected longitudinal portions. Especially, it may be preferred to be able to control the behavior of the tip of a guide wire or catheter for optimal navigation, e.g. during a FEVAR procedure. Portions of phase change material (PCM- 1,  PCM  2 ) arranged inside a tube material T_M can be activated at selected longitudinal parts of the elongated device.

FIELD OF THE INVENTION

The present invention relates to the field of medical devices. Morespecifically, the invention provides an elongated interventional devicewith variable stiffness, e.g. in the form of a guide wire or catheterwith a variable stiffness of its tip.

BACKGROUND OF THE INVENTION

Catheterization has become one of the most widely used procedures incardiovascular analysis and treatment. For example in abdominal aneurismrepair a stent is placed in an aneurism, which is a weakened part of theabdominal aorta, to prevent further widening and ultimately rupture ofthe aneurism.

In the case of a so-called Fenestrated EndoVascular Abdominal aneurismRepair (FEVAR) procedure, the renal arteries need to be stented as well.Here, a combination of catheters and guide wires is used to bring thestent into position: First a soft guide wire with a pre-formed tip and acatheter are used to navigate to the renal arteries. In this step oftenseveral guide wires, each with a different stiffness, are tried beforethe surgeon succeeds in positioning the tip of the guide wire andcatheter in the renal artery. After this step, while keeping thecatheter in position, the soft guide wire is removed and a stiff guidewire is introduced. When the stiff guide wire is in place, the catheteris removed and a catheter with the stent is railed over the stiff guidewire in order to position the stent in the renal artery. Hereby it isessential that the guide wire is sufficiently stiff in order to be ableto guide the catheter with the stent.

US 2002/0013550 A1 discloses an apparatus having a steerable distal endportion for insertion in the body lumen which comprises a superelasticshape memory member. Heating the superelastic shape memory member insidethe body lumen caused it to increase in stiffness and tend toward amemorized shape, and subsequent discontinuation of heating causes thesuperelastic shape memory member to decrease in stiffness.

WO 2013/116096 A1 discloses methods for determining aggressiveness of acancer and treatment thereof. An apparatus used in these methodscomprises a light source and at least one optical fiber for transmittingthe light. For redirecting the light onto tissue, the optical fiber hasa blazed fiber Bragg grating with obliquely impressed index changes thatare at a non-perpendicular angle to the longitudinal axis of the opticalfiber.

U.S. Pat. No. 5,662,621 discloses a guide catheter, wherein the cathetershaft can be changed between a generally ductile state and a relativelystiff state through exposure to light. The ultraviolet or laserlightrays change the guide catheter from a relatively stiff state to asoftened, ductile state.

US 2008/0019657 A1 discloses a system for diffusing light from anoptical fiber coupled to a light source, comprising a polymer elementadapted to be connected to the optical fiber and having incorporated ascattering element, wherein the scattering element diffuses the light.

US 2004/0106898 A1 discloses a photothermal actuator comprising anoptical fiber bundle, a light inputting apparatus, and a thermalreceiving element. The thermal receiving element is provided on the partof an outer surface of the optical fiber bundle. The thermal receivingelement is heated by absorption of the light so that the thermalreceiving element and the part of the optical fiber bundle arestretched, whereby the optical fiber bundle and a tube, in which theoptical fiber bundle is inserted, are bent.

SUMMARY OF THE INVENTION

Following the above, it would be advantageous to reduce the amount ofsteps needed to bring the stent in place, e.g. in a FEVAR procedure, soas to speed up the procedure to reduce the patient's exposure to harmfulX-rays and contrast agents, and e.g. reduce the risk of errors duringthe procedure.

In a first aspect, the invention provides an elongated devicecomprising:

a phase change material arranged along at least a part of a longitudinalextension of the elongated device, and

an optical fiber arranged in relation to the phase change material so asto allow transmission of light from a proximal end of the optical fiberto at least part of the phase change material for optically providingheat to said at least part of the phase change material to cause said atleast part of the phase change material to change its stiffness from onestiffness value to a different stiffness value, wherein the opticalfiber comprises a plurality of longitudinal portions with tilted orblazed gratings arranged for guiding light in a direction away from thelongitudinal extension of the optical fiber at respective longitudinalportions of the optical fiber, wherein a tilt angle of the gratings isselected so as to guide light of a specific range of wavelengths evenlyalong at least a longitudinal portion of the optical fiber.

Such elongated device is advantageous, e.g. in the form of a guide wireor catheter that can be used e.g. in FEVAR procedures to eliminate theneed for several catheters or guide wires to be used during suchprocedure. It is possible to have a guide wire or catheter which iscapable of changing its stiffness and thus adapt its properties fromsoft to stiff in a controlled manner during the FEVAR procedure, e.g. bycontrolling stiffness independently of several longitudinal segments ofthe guide wire or catheter, especially of the tip region of the guidewire or catheter. This allows the steps of positioning the guide wire orcatheter tip and the subsequent step of railing a stent in position tobe performed with one single guide wire or catheter. Thus, the number ofprocedural steps during a FEVAR procedure can be reduced. Furthermore,with such FEVAR procedure, the patient's exposure to harmful X-rays andcontrast agents during the procedure can be reduced.

Yet further, by using light to control a change in stiffness of thephase change material transmitted by the involved optical fiber(s), theprocedure is MR compatible since the guide wire or catheter can bemanufactured without the need for magnetic materials.

The optical fiber comprises a plurality of longitudinal portions withtilted or blazed gratings arranged for guiding light in a direction awayfrom the longitudinal extension of the optical fiber at respectivelongitudinal portions of the optical fiber. Especially, the gratings atsaid plurality of longitudinal portions of the optical fiber may haverespective unique grating periods, so as to allow light wavelengthdependent activation of phase change material arranged at said pluralityof longitudinal portions. Especially, a tilt angle of the gratings isselected so as to guide light of a specific range of wavelengths evenlyalong at least a longitudinal portion of the optical fiber, differentlyfrom WO 2013/116096 A1, which teaches a particular combination of blazeangle of the grating and wavelength so that the light is redirectedperpendicular to the longitudinal axis of the optical fiber.

The tilted gratings preferably comprise Bragg gratings.

In the following, a number of optional additional features and/orembodiments will be defined.

Preferably, the optical fiber is arranged to transmit light from aproximal end of the optical fiber for providing heat to a plurality ofdifferent portions of phase change material arranged at differentlongitudinal positions of the elongated device. Especially, it ispreferred that these different longitudinal portions can be selected inresponse to the light applied to the proximal end of the optical fiber.This allows controlling stiffness of different longitudinal segments ofa guide wire or catheter, and thus allows an improved way of navigatingsuch guide wire or catheter. Especially, this may be implemented withseparate optical fiber cores arranged for transmitting light torespective longitudinal portions of the phase change material arrangedalong the elongated device. However, one single optical fiber core maybe used to do so, which will be elucidated in the following. Thetiltedor blazed gratings at said plurality of longitudinal portions ofthe optical fiber may be arranged to guide light in a direction awayfrom the longitudinal extension of the optical fiber at respectivedifferent wavelengths of light. More specifically, the phase changematerial may be arranged at least along said longitudinal portions ofthe optical fiber, so as to allow wavelength dependent change ofstiffness of different longitudinal portions of the elongated device.

The elongated device may comprise an elongated tube containing saidphase change material at least at a part of its longitudinal extension,wherein the optical fiber is arranged inside said elongated tube.Especially, the elongated tube may be formed by a thermally conductingmaterial, and wherein portions of phase change material is arrangedwithin the thermally conducting material. Such thermally conductingmaterial may comprise the material Pebax® or e.g. Pebax® filled withthermal conductive ceramic or metal particles for increased thermalconductivity.

The phase change material may be selected such that it increases itsstiffness in response to application of heat, which allows e.g. FEVARprocedure, where the elongated device is preferably relatively soft inthe beginning of the procedure, while it is preferred that at least apart of the elongated device is stiffened to allow railing of a stentinto position. The phase change material should at least have a meltingpoint above body temperature and may comprise at least one of: paraffins(e.g. N-henicosan, tristearin), fatty acids (e.g. lauric acid) or salthydrates. Such materials are known in the art. It is preferred, that themethod is arranged to increase stiffness by a factor of such as 50 inresponse to heat applied by light. The light applied may be in the lightwavelength range of such as 400-2000 nm.

Preferably, at least a part of the phase change material is arrangedalong a distal end portion of the elongated device. Hereby, at least apart of the tip of a guide wire or catheter can be controlled withrespect to stiffness, thus providing improved navigation properties fora user. It may be preferred that the optical fiber is arranged to allowa plurality of different longitudinal portions of the distal end portionof the elongated device to be optically controlled.

The optical fiber may comprise a plurality of optical fiber coresarranged within one common cladding. Especially, at least one of saidplurality of optical fiber cores is arranged to provide light to phasechange material arranged outside said cladding. Especially, at least oneof said plurality of optical fiber cores comprises optical elements isarranged for optical shape sensing. Especially, at least one of theplurality of optical fiber cores arranged within said common cladding isarranged for optical shape sensing, i.e. said at least one optical fibercore has optical element allowing optical interrogation to allowreconstruction of its shape.

The elongated device may be in the form of an interventional guide wireor an interventional catheter.

In a second aspect, the invention provides a system comprising:

an elongated device according to the first aspect, and

a light source arranged for connection to the proximal end of opticalfiber for providing light to cause said at least part of the phasechange material to change its stiffness from one stiffness value to adifferent stiffness value. Especially, the light source is arranged forselection between a plurality of different modes of operations, whereinthe light source provides light with different wavelengths in saiddifferent modes of operations, and wherein the optical fiber of theelongated device is arranged to guide light away from a longitudinalextension at respective different longitudinal positions in responsethereto.

In a third aspect, the invention provides a method for controlling anelongated device, the method comprising:

providing an elongated device according to the first aspect comprisingan optical fiber arranged to transmit light from its proximal end to aphase change material arranged along at least a longitudinal portion ofthe elongated device, and

providing light to a proximal end of the optical fiber, so as tooptically provide heat to said portion of the phase change material tocause said portion of the phase change material to change its stiffnessfrom one stiffness value to a different stiffness value. Especially, themethod may comprise selecting between a plurality of differentwavelengths of light, so as to select where, between a plurality ofdifferent longitudinal portions of the elongated device, to guide lightinto the phase change material, especially the optical fiber comprises aplurality of longitudinal portions with different wavelength dependenttilted Bragg gratings.

In a fourth aspect, the invention provides a FEVAR procedure comprising:

providing an interventional catheter or guide wire comprising anelongated device according to the first aspect,

positioning a tip of the interventional catheter or guide wire in anartery,

applying light to a proximal end of the optical fiber so as to provide astiffening of at least a longitudinal portion of the catheter or guidewire, and

railing a stent over the catheter or guide wire after said stiffening,so as to position the stent in the artery. In case of a phase changematerial that softens when heat is applied, the procedure may be toapply heat, i.e. light, during position of the tip, and then to stop orat least reduce applying light in order to stiffen the tip.

It is appreciated that the same advantages and embodiments of the firstaspect apply as well for the second and third aspect. In general thefirst, second, third, and fourth aspects may be combined and coupled inany way possible within the scope of the invention. These and otheraspects, features and/or advantages of the invention will be apparentfrom and elucidated with reference to the embodiments describedhereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will be described, by way of example only,with reference to the drawings, in which

FIG. 1 illustrates a simple sketch of an embodiment,

FIG. 2 illustrates a sketch of another embodiment,

FIG. 3 illustrates a sketch of an embodiment with tilted gratings withunique periods,

FIG. 4 illustrates a sketch of an embodiment where phase change materialis embedded in a tube around the optical fiber,

FIG. 5 illustrates a cross-sectional sketch of a multi-core embodiment,

FIG. 6 illustrates a graph showing measured light transmission lossspectra versus grating tilt angle for an optical fiber,

FIG. 7 illustrates a system embodiment, and

FIG. 8 illustrates steps of a method embodiment.

DESCRIPTION OF EMBODIMENTS

FIG. 1 illustrates a simple sketch of basic parts of an embodiment, e.g.parts of a medical guide wire or catheter. A portion of phase changematerial PCM is arranged along a part of a longitudinal extension of theelongated device, here illustrated as the distal end portion of theelongated device. An optical fiber OF is arranged to guide light to thephase change material PCM so as to allow transmission of light L from aproximal end of the optical fiber OF to at least part P of the phasechange material PCM for optically providing heat to this part P of thephase change material PCM. Hereby, this part P of the phase changematerial PCM will change its stiffness from one stiffness value to adifferent stiffness value, e.g. from “soft” to “hard”, or the oppositeway. This allows control of the behavior of the elongated device, whichis advantageous e.g. for navigating a guide wire or catheter in aninterventional medical procedure, such as a FEVAR procedure. It is to beunderstood that the light source providing the light L and the phasechange material PCM should be matched to allow enough optical heat to betransmitted to the phase change material PCM to make it change from onephase to another phase.

In the illustration of FIG. 1, light L is guided longitudinally in theoptical fiber OF until it reaches an optical element which guides thelight L out of the optical fiber OF an into the phase change materialPCM that surrounds the optical fiber OF. This can be obtained bygratings. Especially, it is preferred that the optical fiber OFcomprises optical elements arranged at respective longitudinalpositions, so as to enable independent control of multiple segments ofthe catheter with the use of a single optical fiber OF. Hereby, anincreased navigation of the elongated device can be obtained.

FIG. 2 illustrates another sketch of an optical fiber OF into whichlight L is applied to one end. By means of tilted or blazed Bragggratings F_BG, a portion of the light L_P is guided out of the opticalfiber, i.e. in a direction away from a longitudinal extension of theoptical fiber OF, e.g. perpendicular to the longitudinal extension ofthe optical fiber OF. Similar to reflection of light with a wavelengthmatching the Bragg condition in a conventional Bragg grating, lightwhich otherwise would be reflected in the fiber core is partly or fullycoupled into the cladding CLD (guided cladding modes) and partly intoradiation modes, and hence is coupled out of the optical fiber OF. Thisallows control of the longitudinal position where light is guided out ofthe optical fiber OF and thus into surrounding or adjacently positionedphase change material (not shown in FIG. 2).

FIG. 3 illustrates how the above principle of guiding light out of anoptical fiber OF by means of gratings F_BG can be extended to provideposition or longitudinal control of where light is guided out of thefiber OF, and thus into adjacently positioned phase change material (notshown in FIG. 3). By varying the grating period along the length of theoptical fiber OF (chirped grating), or by having several segments oftilted Bragg gratings F_BG with a unique grating period, the locationalong the length of the optical fiber OF at which the light is trappedout can be controlled by adapting the wavelength of the light sourceproviding light to the proximal end of the optical fiber OF. Thedifferent grating periods of the gratings F_BG is indicated by thelengths of the double arrows which are seen to increase from the oneF_BG to the left which has a short grating period, to the one F_BG tothe right which has a longer grating period. This allows longitudinalposition control of the stiffness of the elongated device by means ofvarying the wavelength of light applied.

There are several approaches to heat up the phase change material. Oneway is to adapt the cladding such that it has a high absorptioncoefficient such that it heats up by the light that is coupled into thecladding. Heat could be transferred by thermal conduction from thecladding to the phase change material. For this, it is essential thatthere is good thermal contact between the cladding and the phase changematerial. Another approach is to remove the cladding from the opticalfiber such that the light is not coupled into cladding modes but intoradiation modes. For this, it is important for a proper effect, that thephase change material surrounding the optical fiber core has a highabsorption coefficient such that the light is converted into sensibleheat. This could for example be achieved by adding a black absorber(such as black carbon particles) to the PCM.

FIG. 4 illustrates an optical fiber OF arranged in a cladding CLD, whichis again arranged within a tube of a tube material T_M, e.g. Pebax® orPebax® filled with thermal conductive ceramic or metal particles, whichhas a high thermal conduction effect. Blocks of phase change materialPCM_1, PCM_2 is embedded or integrated in the tube material T_M. In theoptical fiber OF tilted gratings are indicated at positionscorresponding to the longitudinal positions of the blocks of phasechange materials PCM_1, PCM_2. These gratings are indicated to havedifferent grating periods, thus allowing selection between activatingphase change of PCM_1 and PCM_2 by correspondingly providing light by amatching wavelength.

FIG. 5 illustrates a cross-sectional of a specific embodiment with anoptical fiber having a plurality of optical fiber cores OSS_C, C_STarranged within one common cladding CLD and jacket JKT. Especially, suchmulti-core optical fibers are used in a technique known as Optical ShapeSensing (OSS), where optical interrogation of strain sensing opticalelements in the optical fiber core(s) is used to provide reconstructionof the shape of an optical fiber, and thus the shape of an elongateddevice in which such optical fiber is positioned.

In the illustrated example, stiffening of an elongated device by meansof phase change material is combined with OSS for shape sensing. In theshown example, three of the optical fiber cores C_ST are arranged forproviding light to phase change material arranged (not shown) outsidethe jacket JKT of the optical fiber, while four fiber cores OSS_C arearranged for OSS. Such combination of stiffness control and OSS isadvantageous for providing a compact (thin) medical interventionalinstrument. Such instrument allows a user to navigate the instrument bymeans of the stiffening control feature, and at the same time,navigation is made easy by means of the OSS facility that can allow theuser to real-time monitor e.g. the 3D position of the tip of theinstrument.

FIG. 6 shows a graph of transmission loss TL experimentally measured foran optical fiber with tilted gratings. The transmission loss TL spectra(wavelength detuning) W_D is shown versus tilt angle T_A (in the angleinterval 0°-15°) of the tilted gratings. The bandwidth and the amount oftrapped out light depends on the tilt angle T_A of the grating planes,as can be seen. This means that the tilt angle T_A can preferably bechosen in such a way that all light of a specific range of wavelengths(peak wavelength+bandwidth) is evenly distributed along the targeted PCMsegment. Also, the difference between the periods of the gratings shouldbe sufficiently large, and hence also the bandwidth of the light source,such that each segment can be addressed individually.

In general, tilt angles in the range of 5° to 45° may be preferred. Ingeneral, light within the wavelength range of 400 nm to 2000 nm may bepreferred for activating a change of phase in the phase change material.

FIG. 7 shows a simple block diagram of parts of a system embodiment,e.g. a medical system for performing a FEVAR procedure. A guide wire GWcomprising an elongated device as explained above including an opticalfiber arranged for applying heat to preferably a plurality of differentportions of phase change material arranged along the guide wire GW toselectively allow stiffening of the different portions of phase changematerial the elongated device. A light source C_LS is arranged forconnection to the proximal end of optical fiber in the guide wire GW.This light source C_LS serves to provide light to cause the selectedportion of phase change material to change its stiffness from onestiffness value to a different stiffness value. The light source C_LS iscontrolled by a processor P in accordance with a user input U_I.Especially, this user input U_I is obtained from a control deviceallowing a user to control the stiffness of selected parts of the guidewire to facilitate navigation, e.g. as part of a FEVAR procedure. Theprocessor P executes a control algorithm that translates the user inputU_I into e.g. a light wavelength to be applied by the light source C_LS,so as to activate the desired parts of phase change material in theguide wire GW in order to obtain behavior of the guide wire GW accordingto the user input U_I.

Especially, the guide wire GW may comprise optical fiber cores arrangedfor application of OSS. In such case, the system may comprise an opticalconsole arranged for optical interrogation of such OSS fiber cores, andaccordingly generation of an image of a reconstructed 3D shape of theguide wire GW.

FIG. 8 shows steps of an embodiment of a method for controlling anelongated device. First step is providing an elongated device P ELcomprising an optical fiber arranged to transmit light from its proximalend to a phase change material arranged along at least a longitudinalportion of the elongated device. Next step is to determine anavigational input D NV from a user. In response to the user input, e.g.longitudinal position where the user want a stiffening of the elongateddevice, a step of determining a light wavelength D_LW to be applied tothe optical fiber is performed. Finally, a step of providing light A_LWto a proximal end of the optical fiber with the determined wavelength isperformed. Hereby, the desired portion of phase change material isoptically heated to cause the desired portion of the phase changematerial to change its stiffness from one stiffness value to a differentstiffness value.

To sum up, the invention provides an elongated device, e.g. aninterventional guide wire or catheter, comprises an optical fiber OFarranged to allow transmission of light to phase change material PCMarranged long the elongated device, for optically heating the phasechange material PCM to change its stiffness from one stiffness value toa different stiffness value. Using distributed tilted or blazed Bragggratings with light wavelength dependent unique grating periods alongthe optical fiber, it is possible to provide a guide wire or catheterwhich can be stiffness controlled at selected longitudinal portions.Especially, it may be preferred to be able to control the behavior ofthe tip of a guide wire or catheter for optimal navigation, e.g. duringa FEVAR procedure. Portions of phase change material PCM_1, PCM _2arranged inside a tube material T_M can be activated at selectedlongitudinal parts of the elongated device. In combination with OpticalShape Sensing, an optimal control of a medical interventional instrumentcan be obtained.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, such illustration and descriptionare to be considered illustrative or exemplary and not restrictive; theinvention is not limited to the disclosed embodiments. Other variationsto the disclosed embodiments can be understood and effected by thoseskilled in the art in practicing the claimed invention, from a study ofthe drawings, the disclosure, and the appended claims. In the claims,the word “comprising” does not exclude other elements or steps, and theindefinite article “a” or “an” does not exclude a plurality. A singleprocessor or other unit may fulfil the functions of several itemsrecited in the claims. The mere fact that certain measures are recitedin mutually different dependent claims does not indicate that acombination of these measured cannot be used to advantage. A computerprogram may be stored/distributed on a suitable medium, such as anoptical storage medium or a solid-state medium supplied together with oras part of other hardware, but may also be distributed in other forms,such as via the Internet or other wired or wireless telecommunicationsystems. Any reference signs in the claims should not be construed aslimiting the scope.

1. An elongated device comprising: a phase change material arranged along at least a part of a longitudinal extension of the elongated device, and an optical fiber arranged in relation to the phase change material so as to allow transmission of light from a proximal end of the optical fiber to at least part of the phase change material for optically providing heat to said at least part of the phase change material to cause said at least part of the phase change material to change its stiffness from one stiffness value to a different stiffness value, wherein the optical fiber comprises a plurality of longitudinal portions with tilted or blazed gratings arranged for guiding light in a direction away from the longitudinal extension of the optical fiber at respective longitudinal portions of the optical fiber, wherein a tilt angle of the gratings is selected so as to guide light of a specific range of wavelengths evenly along at least a longitudinal portion of the optical fiber.
 2. Elongated device according to claim 1, wherein the optical fiber is arranged to transmit light from a proximal end of the optical fiber for providing heat to a plurality of different portions of phase change material arranged at different longitudinal positions of the elongated device.
 3. Elongated device according to claim 1, wherein the tilted or blazed gratings at said plurality of longitudinal portions of the optical fiber are arranged to guide light in a direction away from the longitudinal extension of the optical fiber at respective different wavelengths of light.
 4. Elongated device according to claim 3, wherein the phase change material is arranged along at least along said longitudinal portions of the optical fiber, so as to allow wavelength dependent change of stiffness of different longitudinal portions of the elongated device.
 5. Elongated device according to claim 1, wherein the gratings at said plurality of longitudinal portions of the optical fiber have respective unique grating periods, so as to allow light wavelength dependent activation of phase change material arranged at said plurality of longitudinal portions.
 6. Elongated device according to claim 1, wherein said tilted or blazed gratings comprise Bragg gratings.
 7. Elongated device according to claim 1, comprising an elongated tube containing said phase change material at least at a part of its longitudinal extension, wherein the optical fiber is arranged inside said elongated tube..
 8. Elongated device according to claim 1, wherein phase change material is arranged at least along a distal end portion of the elongated device.
 9. Elongated device according to claims 1, wherein the elongated device is an interventional guide wire or an interventional catheter.
 10. A system comprising: an elongated device comprising: a phase change material arranged along at least a part of a longitudinal extension of the elongated device, and an optical fiber arranged in relation to the phase change material so as to allow transmission of light from a proximal end of the optical fiber to at least part of the phase change material for optically providing heat to said at least part of the phase change material to cause said at least part (P) of the phase change material to change its stiffness from one stiffness value to a different stiffness value, wherein the optical fiber comprises a plurality of longitudinal portions with tilted or blazed gratings arranged for guiding light in a direction away from the longitudinal extension of the optical fiber at respective longitudinal portions of the optical fiber, wherein a tilt angle of the gratings is selected so as to guide light of a specific range of wavelengths evenly along at least a longitudinal portion of the optical fiber, and a light source arranged for connection to the proximal end of optical fiber for providing light to cause said at least part of the phase change material to change its stiffness from one stiffness value to a different stiffness value.
 11. A method for controlling an elongated device, the method comprising: providing an elongated device comprising an optical fiber arranged to transmit light from its proximal end to a phase change material arranged along at least a longitudinal portion of the elongated device, wherein the optical fibers comprises a plurality of longitudinal portions with tilted or blazed gratings arranged for guiding light in a direction away from the longitudinal extension of the optical fiber at respective longitudinal portions of the optical fiber, wherein a tilt angle of the gratings is selected so as to guide light of a specific range of wavelengths evenly along at least a longitudinal portion of the optical fiber, and providing light to a proximal end of the optical fiber, so as to optically provide heat to said portion of the phase change material to cause said portion of the phase change material to change its stiffness from one stiffness value to a different stiffness value. 